Differential Symbiodiniaceae Association With Coral and Coral-Eroding Sponge in a Bleaching Impacted Marginal Coral Reef Environment

Marginal reefs are known for severe stress-inducible perturbations such as high sedimentation, eutrophication, ocean warming, and acidification from anthropogenic climate change. The corals striving in such stressful environments develop physiological adaptations induced by differential genomic expressions or association with thermal stress-tolerant algal symbionts (Symbiodiniaceae). Despite such adaptations, corals are threatened by other space competitors such as algae and sponges. Coral-eroding sponges belonging to the Cliona viridis complex are one such space competitors that also associate with Symbiodiniaceae algal photosymbiont. The diversity of Symbiodiniaceae associates with the coral and sponge from the same ecosystems is scarcely known. In the present study, Symbiodiniaceae community structure in the coral Turbinaria mesenterina, a newly described coral-eroding sponge Cliona thomasi, and their surrounding seawater was determined from the nearshore marginal reef along the central west coast of India. The results revealed a significantly higher relative abundance of Durusdinium and Gerakladium than Symbiodinium and Cladocopium in the seawater. Interestingly, both investigated host species showed differential Symbiodiniaceae association with significantly higher abundance of Durusdinium in coral and Gerakladium in sponge. The beta diversity analysis by Permutational multivariate analysis of variance (PERMANOVA) confirmed significant differences in Symbiodiniaceae profiles between sponge and coral. Durusdinium and Gerakladium are thermotolerant genera known to associate with different hosts in suboptimal conditions. Our field surveys suggested the bleaching resistance of the coral T. mesenterina despite the fact that the sea surface temperature reached the coral thermal threshold of 31°C during different periods of the years 2015, 2016, 2017, 2018, and 2019. Therefore, the thermal tolerance of the investigated coral and sponge species may be attributed to their respective thermotolerant photosymbiont associations. Furthermore, the results also indicated the host-specific photosymbiont selection from the local environment. Although these observations provide valuable biological insight, more research is needed to understand the tripartite association of sponge-coral-symbiont together to evaluate the competitive fitness of holobionts.

Evaluating the feasibility and advantage of a multi-purpose submerged breakwater for harbor protection and benthic habitat enhancement at Kahului Commercial Harbor, Hawai‘i: case study

Construction of breakwaters provides an engineering solution for coastal protection. However, little effort has been made toward understanding the ecological impact on local coral reef ecosystems and developing engineering structures that would enhance the coral reef environment. A submerged breakwater proposed for Kahului Commercial Harbor, Hawai‘i, provided an opportunity to design a multi-purpose ‘reef structure’ to mitigate wave impacts while providing new coral reef habitat. This design involved ecological and environmental considerations alongside engineering principles, serving as a model for environmentally sound harbor development. This field study evaluated environmental conditions and reef community composition at the proposed site in a gradient extending outward from the harbor, using in situ data with multivariate analyses. Benthic and topographic features in the area were assessed using a towed drop camera system to relate to biological factors. Results that support breakwater topography should follow the natural spur and groove and depth of the adjacent reef and orient with wave direction. A deep area characterized by unconsolidated substrata and low coral cover would be replaced with the shallow, sloping hard bottom of the breakwater, and provide an exemplary area for corals to flourish while protecting the harbor from large ocean swells. Surfaces on shallow sloping hard bottoms receive higher levels of irradiance that benefits coral growth. Optimal levels of water motion facilitate sediment removal and promote coral recruitment and growth. The design of the Kahului Harbor submerged multi-purpose structure serves as a model for design of shoreline modification that enhances, rather than degrades, the local coral reef environment.

FORAMINIFERA BENTIK PADA TERUMBU KARANG PULAU BUNAKEN

Study of benthic foraminifera on the coral reefs of Bunaken Island, North Sulawesi Province, was carried out with the aim of providing information regarding the description, distribution and FoRAM Index values on the coral reef environment of Bunaken Island. Sediment sampling in the field was carried out at 5 stations around the island, each area has been plotted on the map, with 3 repetitions and using a SCUBA tool at a depth of 3-8 meters. From observations of sediment surface samples at 15 points in 5 stations spread over Bunaken Island, 5,770 benthic foraminifera specimens have been identified. 81 species from 26 genera of foraminifera were identified and they were then grouped into functional groups to obtain the FoRAM Index. The Index were ranged from 7.18 to 10.5. This indicates that the environment of the coral reef waters around the island is still in good condition. Keywords : Benthic Foraminifera, Coral Reef Ecosystem, Bunaken Island. ABSTRAK Studi foraminifera bentik pada terumbu karang Pulau Bunaken Provinsi Sulawesi Utara dilakukan dengan tujuan untuk menyediakan informasi menyangkut deskripsi, peta sebaran dan nilai FoRAM Index pada lingkungan terumbu karang Pulau Bunaken. Kegiatan pengambilan sampel sedimen di lapangan dilakukan pada 5 stasiun di perairan Pulau Bunaken yang masing-masing areanya telah diplot dalam peta, dengan 3 kali pengulangan dan menggunakan alat SCUBA pada kedalaman 3-8 meter. Dari hasil pengamatan terhadap sampel sedimen permukaan dasar perairan pada 15 titik dalam 5 stasiun tersebar di Pulau Bunaken telah teridentifikasi sebanyak 5.770 spesimen foraminifera bentik. Hasil identifikasi foraminifera tersebut diperoleh 81 spesies foraminifera bentik yang termasuk dalam 26 genus. Spesies-spesies ini kemudian dikelompokkan ke dalam kelompok fungsional untuk mendapatkan FoRAM Index, dan diperoleh kisaran 7,18-10,5. Nilai ini mengindikasikan bahwa lingkungan perairan terumbu karang di sekitar pulau tersebut ada dalam keadaan masih baik dan sehat. Kata Kunci : Foraminifera Bentik, Ekosistem Terumbu Karang, Pulau Bunaken.

Estimation of Sand Distribution in Coral Reef Environment using Colour Segmentation and Colour Thresholding Methods

At present, marine scientists employ manual method to estimate the components in coral reef environment, where Coral Point Count with Excel extensions (CPCe) software is used to determine the coral reef components and substrate coverage. This manual process is laborious and time consuming, and needs experts to conduct the survey. In this paper, a prototype for estimating the distribution of sand cover in coral reef environment from still images by using colour extraction methods was introduced. The colour segmentation called delta E was used to calculate the colour difference between two colour samples. Another method used was colour threshold by setting the range of sand colour pixels. The system was developed by using a MATLAB software with image processing toolbox. The developed system was semi-automatic computer-based system that can be used by researchers even with little knowledge and experience to estimate the percentage of sand coverage in coral reef still images.

Estimation of Coral Rubble Quantity using Edge Detection and Morphological- Based Methods

Reef rubble represents the broken components of the coral and reef structure which could be in the form of dead, broken or other fragmented coral. The process to estimate the distribution of reef rubble is currently done manually and thus takes a long time to complete and is laborious. This paper presents an image-processing-based method to estimate the distribution of reef rubbles in a coral reef environment from a still image. The method is basically a series of image processing steps including image complement, image binarization, edge detection, smoothing by Weiner filter and followed by erosion and dilation process. The experimental results showed that the system was able to roughly estimate the distribution of reef rubble.

Change Detection in Coral Reef Environment Using High-Resolution Images: Comparison of Object-Based and Pixel-Based Paradigms

Despite increases in the spatial resolution of satellite imagery prompting interest in object-based image analysis, few studies have used object-based methods for monitoring changes in coral reefs. This study proposes a high accuracy object-based change detection (OBCD) method intended for coral reef environment, which uses QuickBird and WorldView-2 images. The proposed methodological framework includes image fusion, multi-temporal image segmentation, image differencing, random forests models, and object-area-based accuracy assessment. For validation, we applied the method to images of four coral reef study sites in the South China Sea. We compared the proposed OBCD method with a conventional pixel-based change detection (PBCD) method by implementing both methods under the same conditions. The average overall accuracy of OBCD exceeded 90%, which was approximately 20% higher than PBCD. The OBCD method was free from salt-and-pepper effects and was less prone to images misregistration in terms of change detection accuracy and mapping results. The object-area-based accuracy assessment reached a higher overall accuracy and per-class accuracy than the object-number-based and pixel-number-based accuracy assessment.